 In this video, you will see what happens when an enzyme's environment changes, either too hot or a big change in pH, salt concentration or solvent type, the process called denaturing. The word enzyme means in yeast, where they were first discovered. Zymase, one of the enzymes in yeast, is able to catalyze the conversion of sugar into alcohol and carbon dioxide. Carbon dioxide from this reaction helps bread dough to rise and the ethanol could be the biofuel for Brazilian cars or could be used to make alcoholic drinks. Perhaps the commonest example of denaturing a protein is when you cook an egg. The white of an egg is made of soluble protein molecules called albumin. When heated, these molecules become unraveled and tangled together and the egg becomes solid. So when bread is cooked, the zymase becomes denatured. It loses its specific shape and therefore its activity. It also becomes denatured once the concentration of alcohol reaches about 13% during the fermentation of sugar. This gives us a method for preserving food. Molds and bacteria that cause food to go bad use enzymes to break apart the compounds in the food. Food can be preserved if we can denature their enzymes. So can you think of ways we use to preserve food for a long time? Pause the video whilst you think. The main methods are salting, heating, preserving in acid, like pickling, preserving in alcohol, like wine, freezing. We also preserve food by drying or storing it in sugar. However, these methods do not denature enzymes but work by keeping out water in which mold and bacteria thrive. So why do enzymes unravel like this? Well, the primary structure of proteins is when amino acids, there are 20 to choose from, join with the peptide bond. This coils into a sort of chain held together by the attraction between the amino and carboxylic acid groups, forming their secondary structure, with different R side groups of the amino acids sticking out. Some of these will attract each other and some will repel, enabling the protein to coil up in a very specific 3D shape, its tertiary structure, now able to catalyse a specific reaction in living things. So how does a change in temperature, ionic environment, or solvent cause this tertiary shape of enzymes to be lost? Well, remember that proteins in their secondary and tertiary structure are held by hydrogen bonds and dipoles. These changes work primarily by breaking these weak forces. For example, higher temperatures mean the whole structure is vibrating with more energy, causing the enzyme to unravel. With bread yeast, this happens at around 45 degrees Celsius, but some bacteria, which cause food decay, need to be heated above 100 degrees Celsius to denature their enzymes. Similarly, an increase in concentration of iron such as hydrogen, hydroxide, or salt, or changing the solvent from water, which is strongly polar, to alcohol, will disrupt these dipole forces, causing the enzyme to unfold. Consider a final example, yogurt. Putting friendly yogurt bacteria into milk will quickly drop its pH down to 4, which denatures the digestive enzymes in the yogurt bacteria, but also of any bacteria that fall into the mixture. So making yogurt is a pleasant and useful way of preserving milk. In summary, enzymes are protein molecules folded in a special way to catalyse specific reactions in living cells. Denaturing, caused by changes in temperature, solvent, or ionic environment, is the process by which their shape and therefore their activity is lost. There are various methods of food preservation work by denaturing the enzymes in the mold and the bacteria that cause food to go bad.